1. Field of the Invention
The invention is directed to a circuit breaker in which the arc gases generated during current interruption are used to open the circuit breaker and to propel shutters that cutoff the arc.
2. Background Information
In a common construction of a low voltage air circuit breaker, the movable contact is mounted on a contact arm that is pivoted to open the contacts by a spring powered operating mechanism triggered by a trip unit responsive to an overcurrent condition in the protected circuit. Even though the contacts open, current continues to flow by way of an arc that is struck between the opening contacts. This arc must be extinguished in order to interrupt the current. Typically, the arc is commutated to an arc chute containing a stack of spaced apart electrically conductive plates that break the arc into a series of smaller arcs that raise the arc voltage thereby aiding in termination of the arc. Simultaneously, the arc is cooled by arc gases formed by the vaporization of the contact and surrounding materials and directed to vents in the circuit breaker housing.
One approach to limiting the let through current during interruption has been to speed up the opening of the contacts. This includes forming a reverse current loop in the conductor leading to the fixed contact to generate magnetic repulsion forces that initiate contact arm opening movement before the opening mechanism has time to respond. Supplemental to this, U.S. Pat. No. 6,204,465 suggests providing paddles on the contact arm against which the expanding arc gases act to accelerate contact opening.
Another approach to limiting let through current, and therefore improving the performance of low voltage circuit breakers, has been to physically cut the arc. U.S. Pat. No. 4,801,772 suggests forcing an insulating wedge between the contacts; however, it has proved difficult to completely cutoff the arc and to reset the spring operated mechanism in this arrangement. U.S. Pat. No. 4,700,030 suggests using the arc gases to drive an insulative closed in cylindrical skirt between the contacts to cutoff the arc.
Despite these approaches, there is still room for improvement in the short circuit interruption performance of low voltage air circuit breakers.